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Full text of "The Cambridge Natural History"

vin                              PSITTACOTHERIUM                              191
logical order. The following genera are included by Wortman in
his family Stylinodontidae.
The earliest type of the Ganodonta is the genus Hemiganus,
with but one species, H. otari-idens. This animal lived during
the deposition of the lowest Eocene strata, the Puerco beds of
North America. It was about as big as a fair-sized Dog, and had
powerful jaws. There were at least two pairs of incisors in the
upper jaw, together with powerful canines and the full premolar
and molar formula. In the lower jaw the canines were also
strong, but the incisors are not certainly known to be more than
two pairs. The enamel upon the posterior surface of the canine
is thin, and in the case of the incisors the enamel seems to be
limited to the anterior face. The lower molars are quadrituber-
cular. It is believed from the presence of a suture on the upper
surface of the premaxillary that the snout of the creature was
tubular. The cervical vertebrae, only known by their centra, are
like those of the Armadillos (and for the matter of that of the
Whales) in the great transverse as opposed to the antero-posterior
diameter. The feet are especially compared with those of the
Ground Sloths. The single ungual phalanx is marked by a large
subungual process, which is pierced by a considerable foramen.
The tibia again is to be compared with that of the Armadillos.
In the Upper Puerco (Torrejon) beds the remains of Psitta-
cotherium are found. This genus, when first discovered, was
referred to the Tillodontia by some and to the Ungulates, the
latter being a refuge for indeterminate Eocene mammals, just as
the " Multituberculata " is for similarly-placed Secondary mammals.
It is now known to be clearly a member of the order Ganodonta.
Wortman thinks that there is but one species, P. multi/ragum.
It seems to have had a general aspect much like that of Setni-
ganws—that is judging from the skull—and was not very greatly
different in size. The facial portion of the skull is short, and the
zygoma is deep. The infra-orbital canal is double, a feature which
crops up in the Sloth, and has been mentioned in the later form of
Ground Sloth, Megcdonyx (but it must be remembered that the
same characteristic is not unknown in Rodents). The dentition
is reduced as compared with that of Ifeinigantis, that is to say, as
far as concerns the molars and the incisors. There is but a single
pair of incisors in each jaw; the canines are strong; the premolar
and molar series seem to have been complete in the lower jaw,